Java 8 Lambda Expressions Tutorial

• TOC
• Introduction
• Comparators
• Filtering
• Functions
• Map/Reduce
• Listeners
• DRY

Introduction

The purpose of this tutorial is to show you how to use the new lambda expressions available in JDK 8. You can download the latest build of JDK 8 at http://jdk8.java.net/lambda/.

We are going to start with a simple example. Anyone who has done threading in java is familiar with the Runnable interface, which can be given to a Thread to run the code within the run method on a separate thread. Let's take a look at the old way to do this and the new way. The first variable r1 is an instance of a Runnable interface done the old way, the second variable r2 is how you do it with lambda expressions.

public class ThreadTest {
  public static void main(String[] args) {
    Runnable r1 = new Runnable() {
      @Override
      public void run() {
        System.out.println("Old Java Way");
      }
    };

    Runnable r2 = () -> { System.out.println("New Java Way"); };

    new Thread(r1).start();
    new Thread(r2).start();
  }
}

Notice that we take all of the boilerplate code which we write every time and get rid of it all with a simple expression. In face, the code to start the thread could even be simplified further as:

new Thread(() -> System.out.println("New Java Way")).start();

In the next section, we will show how to use a comparator the Java 8 way.

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